The invention relates to an apparatus for controlling the exhaust gas recirculation rate of an engine with auto-ignition, a throttle device in the exhaust manifold having means of controlling exhaust recirculation in accordance with exhaust gas pressure and operating characteristics. An apparatus of this kind is known in which a predetermined fresh-air component quantity is metered in accordance with the fuel consumption and with the rpm, with the aid of a baffle-type mixture valve for exhaust gas and fresh air. The fundamental concept is the following: The exhaust gas composition in an internal combustion engine has been determined to be dependent on the temperature of combustion, among other factors. As the combustion temperature rises, the toxic exhaust gas component quantity increases, yet the intention is to reduce this quantity. Accordingly, the temperature of combustion must be lowered, and this can be done by reducing the oxygen component quantity of the total cylinder charge. In the known apparatus, the appropriate fresh-air quantity is accordingly metered for a particular fuel quantity (which in turn is associated with the driver's intentions), and the remaining gas charge for the cylinders is furnished from the exhaust gas. This also has the further effect of reducing the toxic gases as a result of the "afterburning" of the recirculated exhaust gas.
Although the known apparatus generally gives acceptable results, still it does not represent an optimal solution to the problems it is intended to solve, because in particular the fresh-air metering is controlled in an open-loop fashion only; or, if a mechanical air flow rate meter is used, the apparatus is not particularly favorable in terms of cost.